A vertical to surface transmission electrophotonic device (defined "VSTEP" hereinafter) in which light is emitted from and received by the device in the vertical direction with respect to a semiconductor substrate is a key device which is indispensable for data transmission among computers and for optical computing therein.
A light emitting device type vertical to surface transmission electrophotonic device (defined "LED-VSTEP" hereinafter) is one of the conventional VSTEPs. In the LED-VSTEP, light emission of spontaneous emission mode occurs in the vertical direction with respect to a semiconductor substrate.
A laser diode type VSTEP of induced emission mode (defined "LD-VSTEP" hereinafter) has also been developed, and is another of the conventional VSTEPs. This LD-VSTEP comprises a cavity formed in the horizontal direction to a semiconductor substrate, and may comprise a reflecting mirror provided to have an angle of 45.degree. relative to an active layer, so that light is emitted in the vertical direction to the substrate, as described on pages 329 to 331 of "Appl. Phys. Lett. " Vol. 54, No. 4 January 1989.
However, the conventional LED-VSTEP has expected disadvantages in that the electrophotonic converting efficiency is not high, frequency response speed is not fast, and output light directivity is not good, because the light emission is of the spontaneous emission mode.
In addition, the conventional LD-VSTEP has disadvantages in that miniaturization is difficult, because a cavity is formed in the horizontal direction to the semiconductor substrate, and light absorption efficiency is low at the same wavelength as an oscillation wavelength, because an absorption layer and an active layer are provided separately from each other. There is a further disadvantage in the conventional LD-VSTEP in that photosensitivity is lowered when devices are connected in cascade.